A continuous hot-dip plating machine is configured to coat a metal strip such as a steel strip with a molten metal such as zinc. The continuous hot-dip plating machine includes rolls disposed in a plating tank storing the molten metal, the rolls including a sink roll for changing a transfer direction of a metal strip, and a pair of support rolls for flattening the shape of the metal strip. The transfer direction of the metal strip diagonally introduced into the plating bath is vertically upwardly changed by the sink roll. The metal strip then passes through between the pair of support rolls to be pulled out of the plating bath. Subsequently, gas is blown onto the surface of the metal strip from gas wiping nozzles disposed at both sides of the metal strip to wipe off extra molten metal adhered on the surface of the pulled-up metal strip, thereby adjusting deposited mass of the molten metal (occasionally referred to as “coating weight” hereinafter).
When the shape of the metal strip is not sufficiently flattened by the support rolls, the metal strip is warped in a width direction of the metal strip after passing through between the support rolls. In this case, since the distance between the gas wiping nozzles and the metal strip varies across the width direction of the metal strip, impingement pressure of the gas against the metal strip becomes uneven in the width direction, thereby possibly making coating weight non-uniform. In order to restrain the coating weight from becoming non-uniform during the continuous hot-dip plating, there have been proposed techniques for flattening the shape of the metal strip using the support rolls.
For instance, it is disclosed in Patent Literature 1 that, in order to inexpensively provide a roll device in a hot-dip plating bath capable of producing a hot-dip steel sheet that is excellent in uniformity of deposited mass of plating by simultaneously eliminating non-uniformity of the plating in both thickness and length directions of the hot-dip steel sheet, at least one of the support rolls positioned immediately above the sink roll is provided by a non-driven roll and a position(s) of at least one of the sink roll and the support rolls is horizontally adjustable.